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Microbial Adaptations to the Psychrosphere/Piezospherejmmb Symposium 93 J. Molec. Microbiol. Biotechnol. (1999) 1(1): 93-100. Microbial Adaptations to the Psychrosphere/PiezosphereJMMB Symposium 93 Microbial Adaptations to the Psychrosphere/Piezosphere review genetic and biochemical studies of pressure Douglas H. Bartlett* adaptation by psychrotolerant/psychrophilic piezophilic Center for Marine Biotechnology and Biomedicine prokaryotes with an emphasis on results obtained from Scripps Institution of Oceanography my lab with Photobacterium profundum. Other reviews University of California, San Diego covering high pressure adaptation by low temperature- La Jolla, CA 92093-0202, USA adapted deep-sea organisms include those written by Bartlett (1992), DeLong (1992), Prieur (1992), Somero (1990; 1991; 1992), Bartlett et al., (1995), Yayanos (1995; 1998), Kato and Bartlett (1997), and within this miniseries Abstract symposium the article by Kato and Qureshi. Low temperature and high pressure deep-sea Basis of Pressure Effects environments occupy the largest fraction of the biosphere. Nevertheless, the molecular adaptations The thermodynamic consequences of changes in pressure that enable life to exist under these conditions remain are straightforward. Elevated pressure promotes poorly understood. This article will provide an overview decreased system volume changes associated with the of the current picture on high pressure adaptation in equilibria and rates of biochemical processes. Thus, life in cold oceanic environments, with an emphasis on the deep sea must entail life at low volume change, or genetic experiments performed on Photobacterium other biochemical adjustments which compensate for the profundum. Thus far genes which have been found or consequences of elevated pressure. The relationship of implicated as important for pressure-sensing or pressure to equilibrium and rate processes can be pressure-adaptation include genes required for fatty expressed mathematically as follows: acid unsaturation, the membrane protein genes toxR and rseC and the DNA recombination gene recD. Many 1) Kp = K1 exp(-P∆V/RT) deep-sea bacteria possess genes for the production ‡ of omega-3 polyunsaturated fatty acids. These could and 2) k p = k1 exp(-P∆V /RT) be of biotechnological significance since these fatty acids reduce the risk of cardiovascular disease and These two equations express the relationship of either the certain cancers and are useful as dietary supplements. equilibrium constant (K) or rate constant (k) of a reaction to pressure, as determined by the size of the volume Introduction change that takes place during either the establishment of equilibrium (∆V) or the formation of the activated complex ‡ Low temperature and high pressure environments (the (∆V ). K1 and k1 are the equilibrium and rate constants, psychrosphere and the piezosphere, respectfully) occupy respectively, at atmospheric pressure; Kp and kp are the the largest fractions of the known biosphere in terms of constants at a higher pressure, R is the gas constant and volume. Within these environments psychrophiles exist T is absolute temperature. Because the equilibrium and which can grow at temperatures as low as -12 °C (Russell, rate constants are related to pressure in a logarithmic 1990), and piezophiles (also termed barophiles) exist which fashion, seemingly small changes in volume can lead to can grow at pressures as high as 130 megapascal large changes in K or k. For example, a volume change of [Yayanos, 1998; 1 megapascal (MPa) = 10 bar ≅ 9.9 +50 cm3mol-1 will lead to a 89% inhibition of a rate (or 89% atmospheres]. The lower temperature limit is apparently change in K value) at 100 MPa pressure. A volume change set by the freezing temperature of intracellular water, of +100 cm3mol-1 will lead to a 35% decrease in k or K at whereas the upper pressure limit for life is not known. 10 MPa, and >99% decrease at 100 MPa. Volume changes Although Archaea, particularly those belonging to the accompanying many biological processes (both equilibria nonthermophilic branch within the Crenarchaeota kingdom, and reaction rates) are in the range of approximately 20- are highly abundant in low temperature and high pressure 100 cm3mol-1. Therefore, pressure changes can lead to environments (Fuhrman et al., 1992; DeLong et al., 1994), very substantial alteration (decrease or increase) of all of the cultured psychrotolerant/psychrophilic piezophilic biological activities and structures in the absence of prokaryotes fall within well known lineages of the Bacterial adaptation. domain. Results to date indicate that the adaptations that Because water itself is not highly compressible (about enable these deep-sea microorganisms to grow under low 4% per 100 MPa pressure), the effects of increased temperature and high pressure conditions entail subtle pressure on biochemical processes are not due to effects variations of certain regulatory processes and aspects of stemming from compression of the aqueous medium. cellular architecture present in mesophiles. Here I will briefly However, water structure is very important in pressure sensitivity because changes in hydration of macromolecules and metabolites can lead to substantial *For correspondence. Email [email protected]; Tel. 619-534-5233; Fax. 619-534-7313. alterations in system volume. © 1999 Horizon Scientific Press Further Reading Caister Academic Press is a leading academic publisher of advanced texts in microbiology, molecular biology and medical research. 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Thus, pressure is both acclimatory changes thought to be important for growth at a unique and a fundamental thermodynamic parameter. either low temperature or high pressure, membrane fatty acid alterations have received the most attention (Russell Identification of Pressure Sensitive and Hamamoto, 1998; Yayanos, 1998). Both decreased Processes in Mesophilic Microorganisms
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